1. Field of the Invention
The present invention generally relates to the electronics industry and, more specifically, to radio transceiver systems. The present invention more specifically relates to the forming of a coupler in a package.
2. Discussion of the Related Art
A coupler is generally used to recover part of the power present on a so-called main or primary transmission line to provide it to another so-called coupled or secondary line, located nearby. Couplers are divided in two categories according to whether they are formed of discrete passive components (lumped element couplers) or of conductive lines close to one another to be coupled (distributed couplers). The present disclosure relates to the second category of couplers. The ports of the main line are generally called IN (input) and OUT (output). Those of the coupled line are generally called CPL (coupled) on the side of terminal IN and ISO (isolated) on the side of terminal OUT.
Distributed couplers are generally made in the form of conductive lines on a thin insulating substrate. Resistive elements forming attenuators may also be integrated with the coupler. Once completed, the assembly is encapsulated in a package provided, for example, with conductive bumps of connection to an electronic circuit board.
When formed on the substrate, the conductive lines of the coupler are generally surrounded with a ground plane.
The present inventors have noticed that this ground plane has an impact on the coupler performance, and especially on its directivity, which corresponds to the difference in transmission loss between ports ISO and CPL, from port IN. Further, the size of the conductive bumps also has an influence upon this performance. The larger the bumps, the poorer the directivity.